This application is based on and claims priority under 35 U.S.C.xc2xa7119 with respect to Japanese Patent Application No. 11(1999)-264829 filed on Sep. 20, 1999, the entire content of which is incorporated herein by reference.
This invention generally relates to a brake device. More particularly, the present invention pertains to a hydraulic pressure brake device for vehicles having a vacuum boosting mechanism and a hydraulic pressure boosting mechanism as a brake booster for actuating a brake master cylinder in response to brake pedal operation.
A hydraulic pressure brake device having a vacuum booster and a hydraulic pressure boosting mechanism as a brake booster is disclosed in a Japanese Patent Application published as a Toku-Kai-Sho No. 52 (1977)-4969.
In this device, the vacuum booster and the hydraulic pressure booster are combined as a brake booster for an automobile to output an increased boosted power to assist the generation of the brake pressure upon operation of a brake pedal.
The booster device disclosed in this publication has a reaction force mechanism in each of the vacuum and hydraulic pressure boosters. By using such reaction force mechanisms of this booster device, separate stepped booster ratios can be obtained at a high pressure stage of a braking force and at a lower pressure stage of a braking force, with the stepped booster ratio at the lower pressure stage of a braking force being different from the high pressure stage.
A power steering pump is used as the brake pressure source for this booster. The power steering pump supplies brake pressure to the brake boosters.
Another known type of booster is disclosed in a U.S. Pat. No. 3,967,536. The disclosed brake booster device includes a pneumatic power brake device (vacuum brake force boosting mechanism) and a hydraulic pressure power brake device using a power steering pump as the brake pressure source. The brake booster device further includes an auxiliary brake pressure source which can be used when the engine is stopped. More specifically, the brake booster device includes an electrically operated pump as the auxiliary brake pressure source, a pressure response switch disposed between the power steering gear and the pump to actuate the pump by actuation of the pressure response switch.
In a vehicle with a heavier weight, in order to assure a large braking force in the brake system, a boosting force can be added by a hydraulic brake pressure booster immediately after the boosting force limit of the vacuum assisted booster is reached. It is therefore expected to be frequently used if such device becomes practically usable.
The above mentioned boosters are still complex in structure and not yet practical by reason of, for example, a rather complicated delivery pipe system resulting from the use of the power steering pump as an auxiliary brake pressure source for the brake force boosting pressure source.
When using the pump for the power steering device as the brake pressure source, responsiveness particularly at low temperature operation has to be improved.
Further, the brake pressure of the power steering pump is always supplied during the engine operation due to the characteristics of the power steering device, but is not supplied when the engine stops. It is accordingly necessary to use a larger brake pedal operation force when the engine is stopped. For example, if an engine stops on a steep hill and the vehicle has to be stopped, the driver of the vehicle has to depress the brake pedal with a very strong force.
In other words, the power steering pump does not function as a brake pressure source. Since the power steering pump always generates brake pressure, the durability of the pump itself and related parts may be adversely affected.
Because the device disclosed in the aforementioned U.S. patent will not supply brake pressure to the power steering device when the engine stops, the electrically operated pump is added to be driven. This will lead to an expensive system because of the addition of another pump such as the electrically operated pump and will also lead to a complicated delivery hydraulic piping. Further, a properly controlled system is needed to assure the smooth braking operation especially when the change over operation to the hydraulic pressure boosting is carried out.
According to one aspect of the invention, a hydraulic pressure brake device includes a master cylinder that supplies brake pressure from a pressure chamber by driving a piston in the master cylinder in the forward direction in response to the depression of the brake pedal, a vacuum boosting device that assists the movement of the piston in the master cylinder using vacuum boosting in response to the depression of the brake pedal, a pump that supplies brake pressure independently of the operation of the master cylinder, and a hydraulic pressure boosting device that assists the movement of the piston of the master cylinder in response to the brake pedal depression by the brake pressure supplied from the pump. A valve mechanism operable between a first condition in which the boosting force reaches the boosting limit of the vacuum boosting device and a second condition in which the boosting force exceeds the boosting limit of the vacuum boosting device. The valve mechanism prohibits the boosting of the master cylinder piston by the hydraulic pressure boosting device in the first condition and permits the boosting of the master cylinder piston by the hydraulic pressure boosting device in the second condition. A detecting mechanism detects the operating condition of the vacuum boosting device and/or the brake pedal depression amount, with the pump being controlled to be driven by condition detected by the detecting mechanism.
The vacuum boosting device can be defined by a housing in which is positioned a movable wall dividing the housing into a constant pressure chamber connected to a vacuum source and a variable pressure chamber connected to atmospheric pressure, a control valve movable with the movable wall and supported on the housing, and a control valve mechanism controlling the communication between the variable pressure chamber and the atmospheric pressure and the communication between the constant pressure chamber and the variable pressure chamber. In addition a driving mechanism is driven to move the master cylinder piston in response to the pressure differential between the constant pressure chamber and the variable pressure chamber caused by the operation of the control valve mechanism. A first transmitting element is disposed between the brake pedal and the master cylinder piston through the valve mechanism and a second transmitting element transmits the operational force of the driving mechanism to the master cylinder piston by the pressure differential between the constant pressure chamber and the variable pressure chamber. The valve mechanism is controlled by the relative movement of the first transmitting element and the second transmitting element, so that when the pressure differential between the constant pressure chamber and the variable pressure chamber is below a predetermined value, the valve mechanism is in the first condition and when the pressure differential between the constant pressure chamber and the variable pressure chamber exceeds the predetermined value the valve mechanism is in the second condition so that the brake pedal and the master cylinder piston are engageable for force transmission through the valve mechanism and the first transmitting element.
In addition, the hydraulic pressure brake device further includes an elastic member disposed between the second transmitting element and the driving mechanism, with the first transmitting element being directly connected to the brake pedal not via the elastic member. The end of the vacuum boosting device can be provided with a larger diameter portion, with a pair of hydraulic chambers being defined between the larger diameter portion to form the hydraulic pressure boosting device. A communication passage hydraulically communicates the pair of hydraulic chambers, with the valve mechanism being formed to open the communication passage when the pressure differential between the constant pressure chamber and the variable pressure chamber is below the predetermined value and to close the communication passage when the pressure differential between the constant pressure chamber and the variable pressure chamber exceeds the predetermined value. The valve mechanism includes a valve seat element provided in a recess formed at the rear end of the master cylinder piston and a valve body formed at the front end of the first transmitting element.
The hydraulic pressure brake device further includes a power piston provided adjacent the vacuum boosting device side of the master cylinder piston, a pair of hydraulic chambers defined by the front and rear sides of the power piston to form the hydraulic pressure boosting device, and a communication passage for effecting communication between the pair of hydraulic chambers. The valve mechanism opens the communication passage when the pressure differential between the constant pressure chamber and the variable pressure chamber is below the predetermined value and closes the communication passage when the pressure differential between the constant pressure chamber and the variable pressure chamber exceeds the predetermined value.
The hydraulic pressure brake device can also be constructed to include a power piston integrally formed with the second transmitting element and a communication passage formed in the power piston. A detecting mechanism includes a brake pedal operation sensor for sensing the amount of the pedal operation which is compared with a predetermined value. The operation of the pump stops when the detected amount of the pedal stroke is lower than the predetermined value and drives the pump when the detected amount of the pedal stroke exceeds the predetermined value.
The brake pedal operation sensor, which can be a stroke sensor that detects the brake pedal stroke, a brake pedal depression sensor that detects the depression force of the brake pedal, and a pressure sensor that detects the output hydraulic pressure of the master cylinder, can be used to judge the initiation of the driving of the pump based on the detected output of the stroke, the depression force, and the master cylinder hydraulic pressure, either individually or in combination.
The judgment value for initiating the pump driving operation is set immediately before the limit of the boosting force of the vacuum boosting device is reached to assure the smooth movement at the time of adding the hydraulic pressure boosting force of the hydraulic pressure boosting device.
The hydraulic pressure brake device can also be provided with a pressure sensor detecting the pressure in the variable pressure chamber of the vacuum boosting device, with the detected pressure value being compared with a predetermined value to stop the driving of the pump when the detected pressure value is below the predetermined value and driving the pump when the detected pressure value exceeds the predetermined value.
The judgment regarding initiation of the pump driving is made by the detected output of the pressure value or the differential value. The judgment value for initiating the pump driving is set immediately before the limit of boosting force of the vacuum boosting device in order to assure the smooth movement at the time of adding the hydraulic pressure boosting force of the hydraulic pressure boosting device.
According to another aspect of the invention, a hydraulic pressure brake device includes a master brake cylinder having a master cylinder piston and a pressure chamber for outputting hydraulic brake pressure in response to brake pedal operation, a vacuum boosting device which performs a vacuum boosting operation up to a boosting limit to boost operation of the master cylinder piston in response to the brake pedal operation, a pump for outputting hydraulic brake pressure independently of the master brake cylinder, a hydraulic boosting device which performs hydraulic boosting operation to boost the operation of the master cylinder piston by the hydraulic pressure output from the pump, a detecting mechanism for detecting a condition of at least one of the vacuum boosting device and the brake pedal, and a valve prohibiting the hydraulic boosting operation by the hydraulic boosting device during the vacuum boosting when the vacuum boosting is less than the boosting limit of the vacuum boosting device and for allowing the hydraulic boosting operation by the hydraulic boosting device when the vacuum boosting by the vacuum boosting device exceeds the boosting limit of the vacuum boosting device. The pump is adapted to be driven based on the condition detected by the detection mechanism.